NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Doug MacPherson
Date: 2012 Dec 27, 15:25 -0800
What edition of Bowditch are you referring to?
My 1938 copy has the following on Page 180 under "The Sumner Line":
"....The usual method adopted (for finding the LOP) where a 'time sight' is computed is to assume a latitude, then work a longitude and an azimuth. This gives one point on the position line. The line of position is then drawn through the the determined point at right angles to the direction of the azimuth.
"...Where a reduction to the meridian is used, a longitude is assumed and a latitude and azimuth are computed. The line of position is then drawn through this determined point at right angles to the direction of the azimuth."
It would be interesting (and disconcerting) to think that more recent editions have eliminated these techniques for finding an LOP.
As I continue to work with Hansen's tables and Norie's I become more impressed with Norie's. The ABC tables are a snap. The Ex-meridian tables are short yet very comprehensive. The Logs of Trig Functions and and Haversine tables are very easy to use (easier than my 1938 Bowditch). It has become my go to, one book solution.
I have not yet recieved my Martelli tables. Will be interested to see how much quicker they make a time sight than using Norie's.
Now, if I could just get Norie's to fit in my sextant case :)
Cheers,
Doug
Dave,
Martelli works as a sight reduction method by providing a longitude for the DR latitude which becomes a Sumner point of the LOP. The LOP is gotten by adding 90 degrees to the azimuth which is then plotted through the Sumner point. This method is something I became aware of only recently. There is no mention of this in Bowditch.
Greg Rudzinski
From: Dave Walden
[NavList] Re: Martelli's Time-Sight Tables
Date: 26 Dec 2012 16:06
While many posts refer to use of Martelli's tables for time sight reduction, others just say sight reduction; I don't recall any mention of this publication and the use of the Martelli tables for line of position:Martelli's Navigational Tables: A Rapid Method of Finding the Position Line and for Solving Spherical Triangle Problems
There are a number of USNI letters describing "how-to" that may have, in fact, led to the above publication.
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